Gear ratio

Olgrey93 · February 6, 2016

I was curious how do I tell what gears I have in my 2014 GMC sle 4x4. I crawled under the truck but couldn't find any markings on the rear diff.

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redwngr · February 6, 2016

Check the codes on the label in the glovebox.

GU4 3.08 ratio

GU5 3.23

GU6 3.42

GT4 3.73

beast 10 · February 8, 2016

Wow I have the 3.08's. I'm a complete noob when it comes to gearing I should have researched that before buying but they say hindsight is 20/20. So if I plan on re gearing what would be my best and cheapest option if I only pull 3500 pounds once or twice a year and I'm staying with 33's and I have the 6 speed ?

Txjose · February 8, 2016

Probably 3.73s but i would go 4.10s

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beast 10 · February 8, 2016

Makes you wonder why GM used a 3.08 in the first place, thanks Txjose time to research .

Txjose · February 9, 2016

Makes you wonder why GM used a 3.08 in the first place, thanks Txjose time to research .

6spd 3.08 is about the same as 3.73 4spd. I think......07softail will chime in he knows his gears lol

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Badass69 · February 9, 2016

In first gear it's the same... anywhere else the mechanical advantage tapers off. It's not horrid but with high ratios like 3.08 the more gears to play with in the trans the better.... and with granny low and 2 overdrives you only have 3 functional driving gears... and in most instances two because second at 2.36 to 1 is too low to back shift into at highway speed. So beyond 2 overdrives while rolling you have a 1.53 to 1 ratio and a 1.15 to 1 ratio... much like a 60e having 1.5 to 1 and 1 to 1.... but the 60e truck still has a 4.10 set in the rear... not 3.08. 3.08 is 3.08... kind of like my 3.23... I just have more gears to play with and more to downshift too. I still would like 3.73 behind my 8 speed.

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LongrangeLauber · February 9, 2016

6spd 3.08 is about the same as 3.73 4spd. I think......07softail will chime in he knows his gears lol

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6 speed 3.08 rear gears is equivalent to the 4l60e with 3.42's. That being said, the 6l80e has a lower first gear so it comes off the line quicker

namanc6 · February 9, 2016

So my 2015 z71 cc came with 3.42 gears. If I wanted to upgrade to 3.73, will the dealership perform the swap? Or should I go to another shop to have the work done? And by doing so, is this a big warranty concern?

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LongrangeLauber · February 9, 2016

So my 2015 z71 cc came with 3.42 gears. If I wanted to upgrade to 3.73, will the dealership perform the swap? Or should I go to another shop to have the work done? And by doing so, is this a big warranty concern?

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One guy in another thread asked the dealership and they wouldn't cover it under warranty even if they had done the swap, and they were gonna charge him 4200 just for the rear! What a rip off!

The steepest gear they make for the new rear ends is a 3.73 (I'm pretty sure), whether you have a 9.5" or 9.76" rear end. You can go steeper if you go aftermarket, but there is a whole thread I created about the swap you would have to do because no aftermarket manufacturer has come out with 9.5" 12 bolt or 9.76" gears yet.

The front gears are the same as previous generations so finding gears for it will be relatively easy. I personally used Yukon gears in my old truck and put them through hell and they held through

Badass69 · February 9, 2016

6 speed 3.08 rear gears is equivalent to the 4l60e with 3.42's. That being said, the 6l80e has a lower first gear so it comes off the line quicker

Not really... it's not a rounded average lol. When you are on the road and cruising where first and second gears in the trans are no longer a factor... you are equivalent to a 4l60e with 3.08s lol. In first gear only you are equivalent to a 4.10 geared 4l60e truck and then it falls off after that.

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Badass69 · February 9, 2016

The rear gears are available for the 9.5" rear ends but nothing beyond the oem 3.73 for the 9.76". You can get aftermarket carriers for the 9.5" as well but they seem limited to a Tru trac and a clutch pack LSD... and then again absolutely nothing but the stock gov bomb for the 9.76". Aftermarket is really dragging ass on this... and I really doubt the 9.76" rear trucks as limited as they are production wise will ever get anything.

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Willshire · February 9, 2016

3.08 is a decent gear for mileage but kinda doggy in 6th (2.0636:1 effective ratio) vs a 2.156:1 in the 4l60 with 3.08's. 3.42's and the 6l80 seem to be a good middle of the road gear between tough enough to pull a heavy load and get decent mileage. Put big tires on, say 35's or greater and the story changes. i think there is enough grunt in a 3.42 to turn 33's easily. I don't see mileage suffering huge with the exception of changes in how the wind reacts with the truck being slightly higher. Once you recalibrate the speedo it's probably close. i made sure i had at least 3.42's when i bought mine.

HondaHawkGT · February 9, 2016

6th is almost useless with the 3.08 unless you're cruising the interstate at 80 mph. With 33's unless I'm on a long, slow descent on the highway I lock out 6th gear.